If you hangout here long enough, you will become one of us and reliably won't matter.
:), I hope not.
I speak from experience, my standards are slipping.
Code I suggest on this forum never has any real tests in it because a) I haven't got the time to do it and b) most people asking for help won't understand anyway and I suspect the experienced guys here do similar. But don't let it creep into your own code and libraries.
As I said above I think there will be no excuses when we start writing code for the Due, it has the resources to include more defensive code.
Interesting document, I just read it. Did you know it was written by me? My full name is James Robert Gray, AKA Jim Gray 
From that document
Availability is doing the right thing within the specified response time. Reliability is not doing the wrong thing.
I aim for reliability, I'm content to stop a system rather than continue with bogus information. Availability implies redundancy which is out of the scope of what I'm doing I think.
Make each module fail-fast -- either it does the right thing or stops.
By that definition my code is "fail-fast", meaning that it's better to stop a system entirely and right away rather than let things propagate and probably get worse.
Processes are made fail-fast by defensive programming. They check all their inputs, intermediate results, outputs and data structures as a matter of course. If any error is detected, they signal a failure and stop. In the terminology of [Cristian], fail-fast software has small fault detection latency.
As I am trying to do.
There have been a few threads asking if Arduino can be used in a commercial environment and my answer has always been "No, not in my opinion" (talking from the software point of view here). I haven't looked for a while now but IIRC things like digitalWrite() blindly index into arrays.
The framework I'm writing (examples above are from it) attempts to address these sorts of issues but it's as much an academic project as anything as to be honest nobody seems to care about such things.
Still it keeps me off the streets at night
Rob